Pre-sulfurization precautions for catalysts

There are requirements for the hydrogen sulfide concentration in the recycle gas during sulfidation, and the emission of hydrogen sulfide leads to sulfur loss.

Do you mean that during the sulfidation process, hydrogen is not introduced into the reaction system from the hydrogen gas distributor in the cold hydrogen tank located in the middle of the reactor? Since the cold hydrogen tanks are generally located in the middle of the reactor, it is necessary to introduce hydrogen and a sulfurizing agent at a certain concentration from the top of the reactor. This allows the gas phase to flow smoothly through both the upper and lower parts of the reactor, ensuring that all of the catalysts can participate in the reaction and undergo complete sulfidation. As for the emission of waste hydrogen, it will certainly lead to a decrease in hydrogen sulfide concentration, resulting in incomplete catalyst reaction.

During the presulfiding process, the hydrogen sulfide content should be between 1% and 0.5%; if it is too high, the amount of DMDS injected must be reduced； If it’s too low, the injection volume needs to be increased. Generally, hydrogen is injected from a recycle hydrogen compressor, which helps to maintain a relatively stable level of hydrogen sulfide in the recycle hydrogen fed into the reactor, thereby allowing for effective control of the pre-sulfidation rate. If hydrogen is injected from the reactor’s cold hydrogen tank, the hydrogen concentration is high and the hydrogen sulfide concentration is low in a small space; as a result, pre-sulfidation progresses unevenly across different bed layers or around their centers, which affects the stability of the pre-sulfidation process. As for the absence of waste hydrogen emissions, the reason is also the issue of hydrogen sulfide content in the recycled hydrogen gas. Generally, the measure to reduce hydrogen sulfide levels is to decrease the amount of DMDS injected, rather than by releasing waste hydrogen. From another perspective, it can also reduce the overall amount of DMDS used, thereby saving costs.

When sulfiding hydrocracking catalysts, it is permissible to inject cold hydrogen in order to control the temperature rise; specific details can be discussed with the catalyst manufacturer

Thank you, I understand. The explanation was very clear. Thank you.

Without injecting cold hydrogen, I believe it helps to prevent uneven distribution of the sulfiding agent (in the dry process), which could lead to varying degrees of catalyst sulfidation. During the initial hydrogen circulation, the concentration of hydrogen is not at the required level, and the hydrogen content is high; this approach helps to avoid localized reduction of the catalyst. Controlling the heating rate is generally achieved by adjusting the amount of dimethyldisulfide injected to regulate the temperature rise.

Not injecting cold hydrogen prevents incomplete sulfidation of the catalyst, while not venting it prevents a low hydrogen sulfide concentration during the sulfidation process.